[1] Mexican Inst Social Secur, Hlth Res Council, Res Unit Reprod Med, Mexico City, DF, Mexico
[2] Mexican Inst Social Secur, Med Unit High Specialty, Gynecol & Obstet Hosp Luis Castelazo Ayala 4, Mexico City, DF, Mexico
[3] Mexican Inst Social Secur, Hlth Res Council, Res Unit Clin Epidemiol, Mexico City, DF, Mexico